Plant Tissues

• The top and bottom of the leaf are covered with a layer of very thin cells called the epidermal cells, that form epidermal tissue. The epidermis protects the surface of the leaf.
• The upper epidermis is transparent, allowing light to pass through to the photosynthetic cells below. The upper epidermis is also covered with a thin layer of oily material called the waxy cuticle that reduces evaporation of water from the surface of the leaf and prevents the leaf from drying out.
• The lower epidermis has tiny pores called stomata which allow carbon dioxide to enter the leaf and oxygen to leave, also helping to control the amount of water vapour that can pass out of the leaf. On either side of the stomata we find guard cells which control the size of the stomata.
• The palisade mesophyll consists of palisade cells that are packed full of chloroplasts
• Underneath the palisade mesophyll there is the spongy mesophyll layer. It is full of air spaces that allow carbon dioxide to diffuse from the stomata through the spongy mesophyll to the palisade cells. Oxygen also diffuses from the palisade cells through the spongy mesophyll to the stomata
• Xylem tissue transports water from the roots to the stem and leaves, some of which is used in photosynthesis. It also transports dissolved mineral ions including magnesium which is used in the making of chlorophyll.
• Phloem tissue transports dissolved sugars produced by photosynthesis from the leaves to the rest of the plant.
• The movement of sugars or other molecules through phloem tissue is called translocation